SAN FRANCISCO -- A man suffered life-threatening injuries after he was hit by a light rail car Wednesday in San Francisco, police said.

It is unknown why the man, identified only as a 29-year-old, walked out onto the rails around 2:12 p.m. as the N-Judah train was crossing 15th Avenue. Police said the man and the second car in the light rail line collided before he fell to the ground.

The man was rushed to San Francisco General Hospital, where he was undergoing surgery for head trauma Wednesday night, police added. He was expected to later be moved to the intensive care unit.